Currently there is renewed interest in the systemic release of mercury from mercury-based dental amalgam restorations and its potential hazard to dental patients. Based on a 1931 study, it is generally believed that the salivary dissolution of mercury from set amalgams is insignificant. The analytical procedure for mercury then employed had a sensitivity of 0.05 mg/25 ml of the saliva sample. More sensitive methods are currently available to measure nanogram quantities of mercury. The objectives of the proposed project are to evaluate the use of an atomic absorption spectrophotometric method for measuring the salivary dissoluation of mercury from set dental amalgams, and to examine the effect of the following parameters on mercury dissoluation: i) time period after amalgam trituration, ii) residence time in salivar, iii) temperature, iv) copper content of alloys, and v) mercury-alloy ratio. The most popular amalgam alloys (2 conventional and 4 high-copper, low Gamma2 phase) will be tested in human saliva in vitro. Two amalgam alloys, one each from conventional and high-copper alloys that exhibit the highest dissolution of mercury in human saliva, will also be studied in an artificial saliva solution for comparative purposes. Such mercury dissolution data should be of value in any assessment of potential toxicity of mercury from dental amalgams in humans. Additionally, the methodology developed should be useful as a general in vitro screening procedure for evaluating the salivary dissolution potential of all existing amalgam alloys and in the development of new alloys for dental restorations. The long-term objectives of these studies include clinical application of the methodology developed in assessing biocompatibility and safety of mercury-based dental amalgam alloys in humans.